Offshore drilling rigs, such as fixed platforms, jack-up platforms, floating and/or semi-submersible platforms, and dynamically positioned drill ships, are used in the production of hydrocarbons from under the floor of large bodies of water. A riser string is typically provided between the floating rig and the wellhead at the ocean floor. A conventional marine riser comprises a cylindrical tube or column made of ferrous metal, e.g., steel, which is positioned vertically between the seabed and a drilling platform at the surface. The riser typically comprises a plurality of sections or joints connected end to end in a string between the surface and the wellbore. An increasing demand for drilling in greater depths of water has required additional riser tube to be used in order to span the distance from the ocean floor to the floating platform.
In one example, the conventional drilling riser concept comprises a main thick-wall tube that is 21-in. OD with welded connections on each end, usually flanges. The kill and choke, booster and hydraulic lines surround the main tube with connections in the flanges and are supported by clamps. Existing equipment allows the extrusion of 36-ft (11-m) tubes with up to 22.4-in. (570-mm) OD and 1.2-in (30-mm) to 1.4-in. (35-mm) wall thickness. Service lines are connected to the main tube using welded clamp bands. Clamps are needed to prevent the service lines from buckling, to block buoyancy module displacement and to provide support for corrosion protection units.